About 50,000 individual aerosol particles from a total of 108 samples collected at six different altitudes above the Southern Bight of the North Sea. Have been analysed using electron probe-X-ray microanalysis. The results of hierarchical cluster analysis on each sample revealed that, for continental air masses, most of the aerosol particulate matter is characterized by high amounts of aluminosilicates, CaSO4 and Fe-rich particles. For western and marine air masses there was no change in the composition of the most abundant particle type with height. This is in connection with the rather mixed nature of the atmosphere. Non-hierarchical cluster analysis showed that the most abundant particle types in this airshed are: aluminosilicates from coal combustion releases, Fe-rich, sea salt enriched with Pb, and organic material associated with residual oil combustion tracers, accounting for 21, 16, 15 and 12% of the total analysed particles, respectively. Almost 60% of the analysed particles is related to combustion or energy-generation processes. Principal factor analysis used on an elemental frequency matrix led to comparable results with principal factor analysis used in combination with cluster analysis. This shows that the method described here is useful for the identification of aerosol sources.